1. Field of the Invention
The present invention relates to a hydraulic transfer method which may be used for, for example, automobile parts and household-electric-appliances for which special surface properties and decorativeness are required. More particularly, the present invention relates to a hydraulic transfer method, which comprises transferring a transfer layer to a metal substrate having a cured coating film layer, such as a precoated metal plate, utilizing water pressure.
2. Description of Related Art
Formed articles used in appliances such as refrigerators and washing machines include, for example, formed articles obtained by coating a formed metal by means of spray coating, and formed articles obtained by forming a metal plate which has been coated in advance called a precoated metal (PCM). With the recent diversification of demand regarding design of metal formed articles, not only the shape, but also the color and the pattern are regarded as being of major importance. It is difficult to decorate a metal formed article with a pattern by conventional methods.
A formed article is decorated with a pattern by a method of applying a printed film onto a metal formed article. In the case of a product whose pattern is replaced within a short period, a film is a simple and advantageous means. However, in the case in which the above method is employed in the manufacture of a product used for long periods, such as appliances, there arises a problem in that the resulting product is not satisfactory in view of durability. Depending on the three-dimensional shape of the metal formed article, it is difficult to apply the film to the formed article and there is a problem in that thread holes of the metal formed article must be trimmed.
Similarly, it is also difficult to provide decoration with finely designed appearance to the precoated metal plate. As proposed in Japanese Unexamined Patent Application, First Publication No. 2001-079456, a uniform spotted pattern is provided with difficulty, and fine decorations such as patterns of gravure printing could not be provided.
The hydraulic transfer method is a method of transferring a patterned decorative layer onto a target body for transfer by floating a substrate film made of a water-soluble or water-swellable resin, which has a patterned decorative layer, on the water surface, activating a decorative layer with a solvent while dissolving or swelling the substrate film, and submerging a target body for transfer in water while pushing the target body for transfer against the substrate film, and is an excellent decoration method which may be used on a wide range of the formed articles as the target body for transfer, and design freedom is high. However, because of complicated steps, its application was limited to the manufacture of high-grade products for which finely designed appearance was demanded.
In the hydraulic transfer method, it is necessary that the target body for transfer be firmly attached to the decorative layer. For example, since a decorative layer such as printing ink or coating film transferred onto a metal material such as a galvanized steel plate has poor adhesion to a metal substrate, there arose problems in that a printed pattern collapsed during the hydraulic transfer and a decorative layer peeled off during washing with water or forming after drying.
As a means for solving the problems of the above hydraulic transfer method, Japanese Unexamined Patent Application, First Publication No. Sho 61-261100 proposes a method of producing an in-mold decorated formed article, which comprises hydraulically transferring a printed pattern layer onto a target body for transfer having a curing resin layer, which is dried but is not completely cured and in a semi- or non-cured state, forming a curable resin layer so as to cover the printed pattern layer, and completely curing the curing resin layer which exists on both surfaces of the printed pattern layer.
Although the method proposed in Japanese Unexamined Patent Application, First Publication No. Sho 61-261100 is a method which can be employed in the case in which hydraulic transfer is carried out immediately after applying a curable resin to a metal substrate as the target body for transfer, there was a problem in that it is difficult to keep the metal substrate coated with the curable resin in the semi- or non-cured state while maintaining a clean and smooth coated surface, and curing of the curable resin proceeds during the storage, thus making it impossible to receive a transfer layer to be hydraulically transferred.
Also Japanese Unexamined Patent Application, First Publication No. Hei 1-22378 discloses a method comprising floating a hydraulic transfer plate made of a water-soluble or water-swellable film having a decorative layer made of a resin, which is cured by irradiation with radiation or heat, on the water surface, so that the water-soluble or water-swellable film in the hydraulic transfer plate faces downward, placing a formed body into water from the upper portion, thereby to firmly attach the hydraulic transfer plate to the outer surface of the formed body and to transfer the decorative layer in the hydraulic transfer plate onto the surface of the outer surface of the formed body, removing the water-soluble or water-swellable film in the hydraulic transfer plate, and irradiating the decorative layer with ionizing radiation or heating the decorative layer according to the kind of the composition in the transferred decorative layer, thereby curing the decorative layer.
However, in the method disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 1-22378, there still remains a problem in that the decorative layer is peeled off during washing with water or forming after drying because of poor adhesion between the layer and the metal substrate.